Scarlet fever is an infection that is caused by a bacteria called streptococcus. The disease is characterized by a sore throat, fever, and a sandpaper-like rash on reddened skin. It is primarily a childhood disease. If scarlet fever is untreated, serious complications such as rheumatic fever (a heart disease) or kidney inflammation (glomerulonephritis) can develop.
Scarlet fever, also known as scarlatina, gets its name from the fact that the patient's skin, especially on the cheeks, is flushed. A sore throat and raised rash over much of the body are accompanied by fever and sluggishness (lethargy). The fever usually subsides within a few days and recovery is complete by two weeks. After the fever is gone, the skin on the face and body flakes; the skin on the palms of the hands and soles of the feet peels more dramatically.
This disease primarily affects children ages two to ten. It is highly contagious and is spread by sneezing, coughing, or direct contact. The incubation period is three to five days, with symptoms usually beginning on the second day of the disease, and lasting from four to ten days.
Early in the 20th century, severe scarlet fever epidemics were common. Today, the disease is rare. Although this decline is due in part to the availability of antibiotics, that is not the entire reason since the decline began before the widespread use of antibiotics. One theory is that the strain of bacteria that causes scarlet fever has become weaker with time.
Causes & symptoms
Scarlet fever is caused by Group A streptococcal bacteria (S. pyogenes). Group A streptococci can be highly toxic microbes that can cause strep throat, wound or skin infections, pneumonia, and serious kidney infections, as well as scarlet fever. The Group A streptococci are β-hemolytic bacteria, which means that the bacteria have the ability to lyse or break red blood cells. The strain of streptococcus that causes scarlet fever is slightly different from the strain that causes most strep throats. The scarlet fever strain of bacteria produces a toxin, called an erythrogenic toxin. This toxin is what causes the skin to flush.
The main symptoms and signs of scarlet fever are fever, lethargy, sore throat, and a bumpy rash that blanches under pressure. The rash appears first on the upper chest and spreads to the neck, abdomen, legs, arms, and in folds of skin such as under the arm or groin. In scarlet fever, the skin around the mouth tends to be pale, while the cheeks are flushed. The patient usually has a "strawberry tongue," in which inflamed bumps on the tongue rise above a bright red coating. Finally, dark red lines (called Pastia's lines) may appear in the creases of skin folds.
Cases of scarlet fever are usually diagnosed and treated by pediatricians or family medicine practitioners. The chief diagnostic signs of scarlet fever are the characteristic rash, which spares the palms and soles of the feet, and the presence of a strawberry tongue in children. Strawberry tongue is rarely seen in adults.
The doctor will take note of the signs and symptoms to eliminate the possibility of other diseases. Scarlet fever can be distinguished from measles, a viral infection that is also associated with a fever and rash, by the quality of the rash, the presence of a sore throat in scarlet fever, and the absence of the severe eye inflammation and severe runny nose that usually accompany measles.
The doctor will also distinguish between a strep throat, a viral infection of the throat, and scarlet fever. With a strep infection, the throat is sore and appears beefy and red. White spots appear on the tonsils. Lymph nodes under the jawline may swell and become tender. However, none of these symptoms are specific for strep throat and may also occur with a viral infection. Other signs are more characteristic of bacterial infections. For example, inflammation of the lymph nodes in the neck is typical in strep infections, but not viral infections. On the other hand, cough, laryngitis, and stuffy nose tend to be associated with viral infections rather than strep infections. The main feature that distinguishes scarlet fever from a mere strep throat is the presence of the sandpaper-red rash.
Laboratory tests are needed to make a definitive diagnosis of a strep infection and to distinguish a strep throat from a viral sore throat. One test that can be performed is a blood cell count. Bacterial infections are associated with an elevated white blood cell count. In viral infections, the white blood cell count is generally below normal.
A throat culture can distinguish between a strep infection and a viral infection. A throat swab from the infected person is brushed over a nutrient gel (a sheep blood agar plate) and incubated overnight to detect the presence of hemolytic bacteria. In a positive culture, a clear zone will appear in the gel surrounding the bacterium, indicating that a strep infection is present.
Although scarlet fever will often clear up spontaneously within a few days, antibiotic treatment with either oral or injectable penicillin is usually recommended to reduce the severity of symptoms, prevent complications, and prevent spread to others. Antibiotic treatment will shorten the course of the illness in small children but may not do so in adolescents or adults. Nevertheless, treatment with antibiotics is important to prevent complications.
Since penicillin injections are painful, oral penicillin may be preferable. If the patient is unable to tolerate penicillin, alternative antibiotics such as erythromycin or clindamycin may be used. However, the entire course of antibiotics, usually 10 days, will need to be followed for the therapy to be effective. Because symptoms subside quickly, there is a temptation to stop therapy prematurely. It is important to take all of the pills in order to kill the bacteria. Not completing the course of therapy increases the risk of developing rheumatic fever and kidney inflammation.
If the patient is considered too unreliable to take all of the pills or is unable to take oral medication, daily injections of procaine penicillin can be given in the hip or thigh muscle. Procaine is an anesthetic that makes the injections less painful.
Bed rest is not necessary, nor is isolation of the patient. Aspirin or Tylenol (acetaminophen) may be given for fever or relief of pain.
If treated promptly with antibiotics, full recovery is expected. Once a patient has had scarlet fever, they develop immunity and cannot develop it again.
Avoiding exposure to children who have the disease will help prevent the spread of scarlet fever.
- An antibiotic that can be used instead of penicillin.
- Erythrogenic toxin
- A toxin or agent produced by the scarlet fever-causing bacteria that causes the skin to turn red.
- An antibiotic that can be used instead of penicillin.
- A serious inflammation of the kidneys that can be caused by streptococcal bacteria; a potential complication of untreated scarlet fever.
- Hemolytic bacteria
- Bacteria that are able to burst red blood cells.
- The state of being sluggish.
- Pastia's lines
- Red lines in the folds of the skin, especially in the armpit and groin, that are characteristic of scarlet fever.
- An antibiotic that is used to treat bacterial infections.
- Procaine penicillin
- An injectable form of penicillin that contains an anesthetic to reduce the pain of the injection.
- Rheumatic fever
- A heart disease that is a complication of a strep infection.
- Sheep blood agar plate
- A petri dish filled with a nutrient gel containing red blood cells that is used to detect the presence of streptococcal bacteria in a throat culture. Streptococcal bacteria will lyse or break the red blood cells, leaving a clear spot around the bacterial colony.
- Strawberry tongue
- A sign of scarlet fever in which the tongue appears to have a red coating with large raised bumps.
For Your Information
- Cecil Textbook of Medicine, 19th ed., edited by James B. Wyngaarden, et. al. New York: W.B. Saunders Company, 1992.
- The Merck Manual of Diagnosis and Therapy, edited by Robert Berkow. 16th ed. Rahway, NJ: Merck Research Laboratories, 1992.
Gale Encyclopedia of Medicine. Gale Research, 1999.